Peritoneal mesothelioma may be described as either wet or dry. A CAT scan is used to differentiate the two types since their appearances differ on the images acquired by the scan. With dry peritoneal mesothelioma, a CAT scan will show multiple small masses or a single dominant and localized mass with little or no fluid build-up. The build-up of fluid is referred to as ascites. With wet peritoneal mesothelioma, a CAT scan will show widespread nodules with ascites, but not a dominant mass. Though fluid build-up may accompany mesothelioma, a fluid analysis is not sufficient to make a definitive diagnosis of mesothelioma. A biopsy is needed to make a definitive diagnosis. 

The peritoneum membrane that lines the abdominal cavity normally produces only a small amount of peritoneal fluid. If excessive fluid buildup is found to be present, it may be removed with a procedure called paracentesis. This procedure is also referred to as an abdominal tap. There are two types of procedures. A diagnostic abdominal tap involves collecting fluid in a syringe and sending it to a lab for testing and analysis. A large volume abdominal tap involves actually draining a buildup of fluid to relieve abdominal pain and discomfort. Paracentesis procedures may be used to identify the cause of fluid buildup, to identify any infected fluid and to drain the fluid. In addition to identifying and removing peritoneal fluid, paracentesis procedures may be used to identify kidney disease, heart disease, pancreatic disease, infections, cancerous tumors, benign tumors, appendicitis, cirrhosis of the liver, and damaged bowels. With the drainage of fluid buildup associated with peritoneal mesothelioma, a needle or catheter is inserted in the peritoneal cavity to remove the fluid.

There is no established staging system for peritoneal mesothelioma. When people speak of stages of this form of mesothelioma, they are referring to a generalized system of staging. This type of generalized system includes categories that may be applied to all forms of cancer. The categories are defined as follows:

 Category 1 - localized lesion that may be able to be completely removed. Category 2 – cancer is contained within the abdominal cavity and doctors are able to remove as much of the visible cancer as possible, but they will not remove all of the cancer.  Category 3 – cancer is contained within the abdominal cavity and it is also invading other organs.Category 4 - cancer extends outside of the abdominal cavity to other organs. 

Surgery alone and chemotherapy alone have shown to be ineffective against peritoneal mesothelioma. New multimodal treatment methods that combine surgery with chemotherapy and/or radiation therapy are offering more promising results. When surgery is used to remove all or part of the cancer in this type of multimodal process, the process is described as cytoreductive or a debulking surgery. Cytoreduction is classified as complete or incomplete follows:

CompleteCC-0- no visible nodules remain.

CC-1- nodules less than 2.5 cm remains. (A size that may be able to be removed by chemotherapy)

Incomplete

CC-2- nodules between 2.5 cm and 5 cm remain.CC-4- nodules greater than 5 cm or a merging of any unresectable nodules remain anywhere within the abdomen or pelvis. Mesothelioma is a relatively new and underreported form of cancer. In the past, it has been misdiagnosed and confused with other types of cancer. It wasn’t until the late 1990s that the US government began to recognize mesothelioma as a separate form of cancer. The various forms of mesothelioma have been equally underrepresented. In the latest report, 1999-2002, on incidences of cancer published by the National Program of Cancer Registries (NPCR), the only type of mesothelioma to be classified as a separate form of cancer is pleural mesothelioma. Peritoneal mesothelioma is grouped with other cancers, namely omentum and mesentery. The NPCR is a collection of data provided by state cancer registries in the US.